Reorder a release store after the operations it protects.

src/core/iomgr/fd_posix.c

@@ -72,6 +72,9 @@ static grpc_fd *fd_freelist = NULL;
 static gpr_mu fd_freelist_mu;
 
 static void freelist_fd(grpc_fd *fd) {
+  // Note that this function must be called after a release store (or
+  // full-barrier operation) on refst so that prior actions on the fd are
+  // ordered before the fd becomes visible to the freelist
   gpr_mu_lock(&fd_freelist_mu);
   fd->freelist_next = fd_freelist;
   fd_freelist = fd;
@@ -92,7 +95,6 @@ static grpc_fd *alloc_fd(int fd) {
     gpr_mu_init(&r->mu);
   }
 
-  gpr_atm_rel_store(&r->refst, 1);
   r->shutdown = 0;
   r->read_closure = CLOSURE_NOT_READY;
   r->write_closure = CLOSURE_NOT_READY;
@@ -104,6 +106,11 @@ static grpc_fd *alloc_fd(int fd) {
   r->on_done_closure = NULL;
   r->closed = 0;
   r->released = 0;
+  // The last operation on r before returning it should be a release-store
+  // so that all the above fields are globally visible before the value of
+  // r could escape to another thread. Our refcount itself needs a release-store
+  // so use this
+  gpr_atm_rel_store(&r->refst, 1);
   return r;
 }